Connectivity between VMs located in the same virtual network, but different cloud services

Hi,

I have the following setup:

VM1a & VM1b in cloud service 1

VM2 in cloud service 2

All three VMs are in the same virtual network.

I am able to enable ICMP in firewall and ping between the VMs inside the same cloud service (VM1a and VM1b). But we are not able to do the same between VMs in different cloud services, even using their internal IP addresses.

How do we go about doing this?

Thanks,

Vijay